Why do you have a coil in your inner ear?


THAT’S THE WHY:LISTEN: if you can hear what is happening around you, it’s thanks in part to a structure in your inner ear called the cochlea. Like many structures in the ear, it has an exquisite shape – in this case it’s a spiral that contains sensory hairs, which play a key role in detecting the sounds coming in through your ear.

But why is it whorled like a snail’s shell? One suggestion has been that the coiled shape is a good space saver, while another contends that the curves could help to boost the response to low-frequency sounds.

And a new study stakes out an argument that the spiral shape could improve the cochlea’s ability to localise sound. The researchers modelled the cochlea as a sensor array and simulated the external sound pressure that the sensory hair cells would perceive directly. They built up acoustic images for a straight cochlea and a spiral cochlea and compared the sound localisation capabilities.

“The results demonstrate that the spiral shape can achieve better vertical sound localisation. The analysis therefore indicates that the cochlear spiral shape might not only have evolved for space conservation reasons but also for possible perceptual benefits,” write the authors in the physics journal EPL (Europhysics Letters)

The simulations made some assumptions about sounds travelling in the ear, and it would also be hard to carry out practical experiments, but the authors note that their study links the geometry of the cochlea to how it performs in the body. “This finding might be helpful in the designs of cochlear implants and echolocation systems,” they write.